[flow] report doc count when uploading file
This fixes #478 There was no `markStarted` and so 'remaining' was always at 0, so the frontend thought the job was done, even though it was getting notification about 'succeeded' in that job increasing
This fixes #478 There was no `markStarted` and so 'remaining' was always at 0, so the frontend thought the job was done, even though it was getting notification about 'succeeded' in that job increasing